EP0808827A1

EP0808827A1 - Production process for aromatic compounds

Info

Publication number: EP0808827A1
Application number: EP97107802A
Authority: EP
Inventors: Isamu Maeda; Hiroshi Sugizawa; Noboru Saito
Original assignee: Nippon Shokubai Co Ltd
Current assignee: Nippon Shokubai Co Ltd
Priority date: 1996-05-21
Filing date: 1997-05-13
Publication date: 1997-11-26
Also published as: CN1170715A; IL120828A0; US5760280A; JPH09309870A

Abstract

A process for producing aromatic compounds comprises the step of carrying out a reaction between an aromatic carboxylic acid and a polyfluorobenzonitrile, thus forming an aromatic nitrile and a polyfluorobenzene. This process can produce the aromatic compounds with few problems in respect to workers' safety and at a low cost when compared with conventional processes, and can convert the starting materials for the reaction into useful substances in almost no vain, and therefore involves little waste.

Description

BACKGROUND OF THE INVENTION

A. TECHNICAL FIELD

The present invention relates to a process for producing aromatic compounds.

B. BACKGROUND ART

As to production processes for an aromatic nitrile that is one of aromatic compounds, there are, for example, known the following processes: 1) a process utilizing a Sandmeyer reaction via a diazonium salt from an aniline compound that is an aromatic primary amine; and 2) a process in which a benzamide compound that is an aromatic primary amide is chemically dehydrated in the presence of phosphorus pentaoxide, acetic anhydride, or the like. Specifically, 2,3,4,5-tetrachloroaniline is, for example, used as the aniline compound that is a starting material in process 1) above (J. Prakt. Chem., 56, 48-66 (1897)), and 2,3,4,5-tetrachlorobenzamide is, for example, used as the amide compound that is a starting material in process 2) above (Chem. Ber., 107, 920-923 (1974)). In these processes, 2,3,4,5-tetrachlorobenzonitrile is obtained as the aromatic nitrile.
However, as to the above-mentioned conventional production processes for aromatic nitriles, because the aniline compound and the benzamide compound themselves, which are used as starting materials, are generally expensive and often difficult to obtain, the production cost tends to be so high that there are difficulties in practical or economical use. In addition, because a stoichiometric amount of high toxic inorganic cyanide compound or chemical dehydrator needs to be used, there are also problems in respect to workers' safety.

SUMMARY OF THE INVENTION

A. OBJECTS OF THE INVENTION

It is an object of the present invention to provide a process which can produce an aromatic nitrile with few problems in respect to workers' safety and at a low cost.
In addition, it is another object of the present invention to provide a production process for aromatic compounds, which process can convert starting materials for reaction into useful substances in almost no vain, and therefore involves little waste.

B. DISCLOSURE OF THE INVENTION

The present inventors worked diligently to solve the above-mentioned problems and encountered some surprising solutions. As a result, they attained the present invention by finding that if an aromatic carboxylic acid, which is low toxic, industrially easily available, and inexpensive, and a specific polyfluorobenzonitrile are used as starting materials for reaction and reacted upon each other, a series of unexpected specific reactions including mutual addition, exchange, and decarboxylation between a carboxyl group of the aromatic carboxylic acid and a nitrile group of the polyfluorobenzonitrile occur to practically give an aromatic nitrile, which is an aromatic compound, and a polyfluorobenzene, which is also an aromatic compound, at a low cost, with ease, and with high yield.
Thus, a process for producing aromatic compounds, according to the present invention, comprises the step of carrying out a reaction between an aromatic carboxylic acid and a polyfluorobenzonitrile, thus forming an aromatic nitrile and a polyfluorobenzene.
The process of the present invention may further comprise the step of isolating the formed aromatic nitrile after the reaction between the aromatic carboxylic acid and the polyfluorobenzonitrile.
The process of the present invention may further comprise the step of isolating the formed polyfluorobenzene after the reaction between the aromatic carboxylic acid and the polyfluorobenzonitrile.
In the process of the present invention, the reaction may be carried out at a temperature of between about 180 and about 300 °C.
In the process of the present invention, the reaction may be carried out while carbon dioxide or both of carbon dioxide and the polyfluorobenzene which form during the reaction are discharged from a reaction system.
The process of the present invention may further comprise the step in which a reaction intermediate that is an adduct from a carboxyl group and a nitrile group, including an adduct from the aromatic carboxylic acid and the polyfluorobenzonitrile and forming in the course of the reaction therebetween, is re-used for a new reaction between an aromatic carboxylic acid and a polyfluorobenzonitrile.
In the process of the present invention, the aromatic carboxylic acid may be 2,3,4,5-tetrachlorobenzoic acid. In the process of the present invention, the polyfluorobenzonitrile may be pentafluorobenzonitrile.
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Although not especially limited, examples of the aromatic carboxylic acid, which is used as a reactant, are benzoic acid, terephthalic add, isophthalic acid, naphthalenemonocarboxylic acid, naphthalenedicarboxylic acid, and nuclear-substituted matters thereof (e.g. methyl-, methoxy-, phenoxy-, chloro-, bromo-, iodo-, and nitro-substituted ones). Of these compounds, chloro-substituted benzoic acids, particularly, 2,3,4,5-tetrachlorobenzoic acid, are especially preferably used, because they can give 2,3,4,5-tetrachlorobenzonitrile that is an aromatic nitrile that is especially important as a starting material for medicines.
Although not especially limited, examples of the polyfluorobenzonitrile, which is used as a reactant, are difluorobenzonitrile, trifluorobenzonitrile, tetrafluorobenzonitrile, nuclear-substituted matters thereof (e.g. chloro-, bromo-, iodo-, and nitro-substituted ones), and pentafluorobenzonitrile. Of these compounds, pentafluorobenzonitrile is particularly preferably used, because, as mentioned below, it can provide pentafluorobenzene that is a polyfluorobenzene that is especially important as a starting material for polymerization catalysts.
Although not especially limited, the ratio of the polyfluorobenzonitrile to the aromatic carboxylic acid is, for example, in a range of about 0.1 to about 10 equivalents, preferably, about 0.5 to about 8 equivalents, more preferably, about 2 to about 5 equivalents, in respect to practical use, for example, in view of apparatus efficiency.
The manner to carry out the reaction between the aromatic carboxylic acid and the polyfluorobenzonitrile is not especially limited and may be either a batch manner or continuous manner. However, a batch manner is preferable in respect to practical use, for example, in view of the conversion of the reactants.
Although not especially limited, examples of the reaction vessel are pressure-resistant reaction vessels such as autoclaves. Of the reaction vessels, constant-pressure reaction vessels are preferable in respect to practical use.
The reaction between the aromatic carboxylic acid and the polyfluorobenzonitrile is preferably carried out under catalyst-free conditions in view of economical advantage or of saving labor for separation purification operations after the completion of the reaction. However, as needed, the reaction may be carried out in the presence of an acid catalyst to promote the reaction. Although not especially limited, examples of the acid catalyst are as follows: inorganic acids, such as phosphoric acid, boric add; solid acids, such as acid clay, acid alumina. Of these catalysts, the solid acids are preferable in respect to practical use, for example, in view of separation purification. The acid catalyst may be used alone or in adequate combinations of two or more thereof.
When the acid catalyst is used, the amount thereof is not especially limited, but the amount is, for example, in a range of about 0.1 to about 10 mol %, preferably, about 0.5 to about 5 mol %, more preferably, about 1 to about 3 mol %, of the aromatic carboxylic acid in respect to economical advantage.
Because the polyfluorobenzonitrile can also serve as a solvent, it is preferable to carry out the reaction between the aromatic carboxylic acid and the polyfluorobenzonitrile with no solvent other than the polyfluorobenzonitrile in view, for example, of saving labor for separation purification operations after the completion of the reaction. However, if need arises, the reaction may be carried out using solvents inert to the reaction, such as aromatic hydrocarbons (e.g. xylene, pseudocumene, durene), high boiling point solvents (e.g. nitrotoluene, benzyltoluene), alone or in adequate combinations of two or more thereof.
When a solvent other than the polyfluorobenzonitrile is used, the amount of this solvent is not especially limited, but the amount is, for example, in a range of about 10 to about 1,000 % by weight, preferably, about 30 to about 500 % by weight, more preferably, about 50 to about 200 % by weight, of the aromatic carboxylic acid in respect to practical use, for example, in view of apparatus efficiency.
The reaction temperature is, for example, in a range of about 180 to about 300 °C, preferably, about 200 to about 280 °C, more preferably, about 220 to about 260 °C, in respect to, for example, the inhibition of side reactions, or the reaction rate.
The reaction duration depends on various factors, for example, the reaction temperature, the presence or absence of the catalyst, the type and amount of the catalyst, the type and composition of the starting materials for the reaction, and therefore is not especially limited, but the reaction duration is, for example, in a range of about 0.5 to about 50 hours, preferably, about 1 to about 30 hours, more preferably, about 2 to about 20 hours, in respect to practical use, for example, in view of the conversion of the reactants.
If the aromatic carboxylic acid and the polyfluorobenzonitrile are reacted upon each other, a mutual addition-exchange reaction between a carboxyl group of the aromatic carboxylic acid and a nitrile group of the polyfluorobenzonitrile occurs as an equilibrium reaction to give an aromatic nitrile. A polyfluorobenzoic acid is also expected to form in this reaction, but the resultant polyfluorobenzoic acid is unexpectedly easily subjected to irreversible decarboxylation during the above-mentioned reaction and thereby rapidly converted into a polyfluorobenzene. Therefore, the present inventors infers that the aromatic nitrile, the polyfluorobenzene, and a reaction intermediate, which is an adduct from a carboxyl group of the aromatic carboxylic acid or polyfluorobenzoic acid and a nitrile group of the polyfluorobenzonitrile or aromatic nitrile, are included as reaction products in a reaction mixture as obtained by the reaction between the aromatic carboxylic acid and the polyfluorobenzonitrile, and that the polyfluorobenzoic acid does not coexist in the reaction mixture.
Thus, in the present invention process, the aromatic nitrile and the polyfluorobenzene are efficiently produced from the irreversible reaction involving the decarboxylation. Because the polyfluorobenzene is also very useful in industries, it can be utilized for various purposes by being recovered from the reaction mixture. Thus, the present invention process can convert the starting materials for the reaction into useful substances in almost no vain, and therefore involves little waste.
As is mentioned above, the decarboxylation occurs in the course of the reaction between the aromatic carboxylic acid and the polyfluorobenzonitrile, thereby giving carbon dioxide and the aforementioned polyfluorobenzene with a boiling point of about 80 to about 90 °C under normal pressure (e.g. pentafluorobenzene has a boiling point of about 85 °C under normal pressure). Therefore, in the case where a reaction vessel that is closed up tight is used, the reaction pressure increases with the progress of the reaction. The level of the reaction pressure in such a case, depending on the reaction temperature and the space volume ratio of the reaction vessel, might reach about 50 kg/cm², for example, within the aforementioned reaction temperature range. Therefore, considering the pressure resistance of the reaction vessel, it is preferable that the reaction is carried out while carbon dioxide or both of carbon dioxide and the polyfluorobenzene which form during the reaction are discharged from a reaction system. If the reaction is carried out in such a way, the reaction pressure can be suppressed, for example, to not higher than about 10 kg/cm².
For the purpose of more increasing the product yield, the present invention production process may further comprise the step in which a reaction intermediate that is an adduct from a carboxyl group and a nitrile group, including an adduct from the aromatic carboxylic acid and the polyfluorobenzonitrile and forming in the course of the reaction therebetween, is re-used for a new reaction between an aromatic carboxylic acid and a polyfluorobenzonitrile. Such a re-using step can increase the product yield and therefore is very advantageous in industrial practical use.
The aromatic nitrile and the polyfluorobenzene, formed by the reaction between the aromatic carboxylic acid and the polyfluorobenzonitrile, can be easily separated and purified by conventional methods, for example, distillation, extraction, crystallization, after the reaction has finished.

(Advantages of the Invention):

In the present invention production process, because an aromatic carboxylic acid and a polyfluorobenzonitrile were reacted upon each other, an aromatic nitrile and a polyfluorobenzene can be produced with ease and with high yield. Because the aromatic carboxylic acid, which is used as one of the starting materials for the reaction, is low toxic and because the other starting material for the reaction, namely, polyfluorobenzonitrile, is also relatively low toxic, only a little careful consideration for workers' safety is needed. The above-mentioned starting materials for the reaction are both easy to industrially obtain, so the aromatic nitrile and the polyfluorobenzene can be produced practically and at a low cost.
The resultant aromatic nitrile is useful as a starting material for organic synthesis, and polychlorobenzonitriles, particularly, 2,3,4,5-tetrachlorobenzonitrile, are especially important as starting materials for medicines and agricultural chemicals.
In the present invention, the polyfluorobenzene as well as the aromatic nitrile is obtained. The polyfluorobenzene is useful as a starting material for organic synthesis, and, particularly, pentafluorobenzene is important as a starting material for polymerization catalysts. Accordingly, the present invention process can convert the starting materials for the reaction into useful substances in almost no vain, and therefore involves little waste.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention is more specifically illustrated by the following examples of some preferred embodiments in comparison with comparative examples not according to the invention. However, the present invention is not limited to the below-mentioned examples.

EXAMPLE 1

First, 4.5 g (17.3 mmol) of 2,3,4,5-tetrachlorobenzoic acid and 13.4 g (69.4 mmol) of pentafluorobenzonitrile were placed into a small-sized autoclave of 100 ml in capacity made of Hastelloy C and equipped with a stirrer. The inner atmosphere of the autoclave was replaced with a nitrogen gas of atmospheric pressure, and then the autoclave was heated at 230 °C for 6 hours in a closed-up state, whereby the reaction pressure gradually increased up to 9.5 kg/cm² with time. However, after the completion of the reaction, the pressure fell to 2.5 kg/cm² at 20 °C. Thus, a reaction mixture was obtained in a yield of 17.3 g.
The reaction mixture was analyzed by ¹H-NMR and ¹⁹F-NMR. As a result, the conversion was 98 % based on the original molar number of 2,3,4,5-tetrachlorobenzoic acid. In addition, 2,3,4,5-tetrachlorobenzonitrile and pentafluorobenzene were formed in yields of 86 % and 74 % respectively, and the rest of the products was a reaction intermediate, and no pentafluorobenzoic acid was detected.
Next, 17.0 g of the reaction mixture was distilled under normal pressure to obtain pentafluorobenzene in a yield of 2.0 g as a fraction having a boiling point of 80 to 90 °C. Subsequently, the residual liquid was subjected to crystallization filtration at 5 °C to obtain 2,3,4,5-tetrachlorobenzonitrile in a yield of 3.2 g in terms of solid content.
Furthermore, the filtrate was distilled under a reduced pressure of 20 mmHg to obtain pentafluorobenzonitrile in a yield of 10.0 g as a fraction having a boiling point of 50 to 60 °C, and the amount of the balance was 1.8 g.
The analysis showed that the purity of each product was 95 % and the recovery was 92 %, and that the balance was mainly an adduct that was a reaction intermediate.

EXAMPLE 2

The reaction was carried out in the same way as of Example 1 except that 1.5 g of the adduct, which was a reaction intermediate as obtained in Example 1, was added.
As a result, the reaction pressure reached 11.5 kg/cm² during the reaction and fell to 3.0 kg/cm² at 20 °C after the completion of the reaction, and the conversion was 98 %. In addition, the yields of 2,3,4,5-tetrachlorobenzonitrile and pentafluorobenzene were 92 % and 90 % respectively, and no pentafluorobenzoic acid was detected.
Thus, the re-using of the reaction intermediate greatly increased the yields of the objectives.

EXAMPLE 3

The reaction was carried out in the same way as of Example 1 except that the reaction temperature was changed to 200 °C.
As a result, the reaction pressure reached 3.5 kg/cm² during the reaction and fell to 1.0 kg/cm² at 20 °C after the completion of the reaction, and the conversion was 77 %. In addition, the yields of 2,3,4,5-tetrachlorobenzonitrile and pentafluorobenzene were 33 % and 20 % respectively, and no pentafluorobenzoic acid was detected.

EXAMPLE 4

The reaction was carried out in the same way as of Example 1 except that the amount of 2,3,4,5-tetrachlorobenzoic acid was changed to 9.0 g (34.6 mmol).
As a result, the reaction pressure reached 13.5 kg/cm² during the reaction and fell to 4.5 kg/cm² at 20 °C after the completion of the reaction, and the conversion was 98 %. In addition, the yields of 2,3,4,5-tetrachlorobenzonitrile and pentafluorobenzene were 84 % and 65 % respectively, and no pentafluorobenzoic acid was detected.

EXAMPLE 5

The reaction was carried out in the same way as of Example 1 except that 2,3,4,5-tetrachlorobenzoic acid was replaced with 2.7 g (17.3 mmol) of p-chlorobenzoic acid.
As a result, the reaction pressure was almost the same as that in Example 1, and the conversion was 96 %. In addition, the yields of p-chlorobenzonitrile and pentafluorobenzene were 71 % and 61 % respectively, and no pentafluorobenzoic acid was detected.

EXAMPLE 6

The reaction was carried out in the same way as of Example 4 except that the reaction pressure was regulated to 8 kg/cm² with a constant-pressure apparatus.
As a result, carbon dioxide was discharged from the constant-pressure apparatus during the reaction, and the pressure fell to 2.0 kg/cm² at 20 °C after the completion of the reaction, and the conversion was 98 %. In addition, the yields of 2,3,4,5-tetrachlorobenzonitrile and pentafluorobenzene were 85 % and 70 % respectively, and no pentafluorobenzoic acid was detected.

EXAMPLE 7

The reaction was carried out in the same way as of Example 3 except that the reaction duration was changed to 30 hours.
As a result, the reaction pressure reached 9.0 kg/cm² during the reaction and fell to 2.5 kg/cm² at 20 °C after the completion of the reaction, and the conversion was 97 %. In addition, the yields of 2,3,4,5-tetrachlorobenzonitrile and pentafluorobenzene were 86 % and 76 % respectively, and no pentafluorobenzoic acid was detected.

COMPARATIVE EXAMPLE 1

The reaction was carried out in the same way as of Example 1 except that the reaction temperature was changed to 165 °C.
As a result, the reaction pressure was atmospheric, and the conversion was 33 %. However, none of carbon dioxide, 2,3,4,5-tetrachlorobenzonitrile, and pentafluorobenzene was formed, and only a reaction intermediate was formed, and no pentafluorobenzoic acid was detected.
Various details of the invention may be changed without departing from its spirit not its scope. Furthermore, the foregoing description of the preferred embodiments according to the present invention is provided for the purpose of illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

Claims

A process for producing aromatic compounds, which comprises the step of carrying out a reaction between an aromatic carboxylic acid and a polyfluorobenzonitrile, thus forming an aromatic nitrile and a polyfluorobenzene.
A process according to claim 1, further comprising the step of isolating the formed aromatic nitrile after the reaction between the aromatic carboxylic acid and the polyfluorobenzonitrile.
A process according to claim 1, further comprising the step of isolating the formed polyfluorobenzene after the reaction between the aromatic carboxylic acid and the polyfluorobenzonitrile.
A process according to claim 1, wherein the reaction is carried out at a temperature of between about 180 and about 300 °C.
A process according to claim 1, wherein the reaction is carried out while carbon dioxide or both of carbon dioxide and the polyfluorobenzene which form during the reaction are discharged from a reaction system.
A process according to claim 1, further comprising the step in which a reaction intermediate that is an adduct from a carboxyl group and a nitrile group, including an adduct from the aromatic carboxylic acid and the polyfluorobenzonitrile and forming in the course of the reaction therebetween, is re-used for a new reaction between an aromatic carboxylic acid and a polyfluorobenzonitrile.
A process according to claim 1, wherein the aromatic carboxylic acid is 2,3,4,5-tetrachlorobenzoic acid.
A process according to claim 1, wherein the polyfluorobenzonitrile is pentafluoroberzonitrile.